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Cutting-edge Technology in Radiation Therapy: Helical Tomotherapy Overview

Learn about the advanced features of Helical Tomotherapy, including the machine characteristics and clinical applications for treating cancer patients effectively. Discover how this innovative technology combines image guidance and precise treatment delivery for improved outcomes.

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Cutting-edge Technology in Radiation Therapy: Helical Tomotherapy Overview

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  1. The external beam radiotherapy and Image-guided radiotherapy (3) SomvilaiMayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University

  2. Machine characteristics • 6 MV accelerator • 3.5 MV: MVCT • No flattening filter • Field Size in width: 40 cm • Treatment length: 160 cm 6 MV LINAC 64 leaf MLC Pitch = Distance Traveled Per Rotation Slice Width MVCT detector array

  3. Machine characteristics • TOMO Binary multileaf collimator • Optical sensors and pneumatic driven • Binary 64 leaf MLC • MLC leaf width: 6.25 mm (ISO) • Field Size in length: 1, 2.5 and 5 cm by a set of moveable jaws 100 times faster MLC Speed MLC leaves that move at 250 cm/s to open or shut in 20 milliseconds

  4. Machine characteristics • Treatment is delivered through the full 360° • This is approximated in the planning process • by 51 different beam directions • With a spacing of just over 7° • The rate of movement of the couch, relative to the • thickness of the fan beam, is referred to as the pitch Allows treatment of very long volumes without field junctions Slice width

  5. Helical Tomotherapy Process • Imaging / Contouring • Planning / Optimizing • In-room megavoltage CT imaging • Image Registration (IGRT) • Treatment delivery Adaptive RT: Dose Guidance (Recalculation / Reconstruction ) Dose Modification

  6. Helical Tomotherapy • The complex integrated technologies • With multiprofessional team • Physicist/dosimetrist • Radiation oncologist • Radiation therapist • Radiographer

  7. Helical Tomotherapy Clinical use : Rationale for patient selection • Treat patients who were considered likely to benefit from • IGRT : to inform repositioning • IMRT: complex target volume shapes, adjacent critical normal tissue structures • Combined IGRT/IMRT approach University of Cambridge /Burnet et al. Clinical Oncology 2010;22:294–312

  8. Helical Tomotherapy University of Cambridge /Burnet et al. Clinical Oncology 2010;22:294–312

  9. Helical Tomotherapy Treatment planning • Inverse planned IMRT concepts • Dose volume constraints : typically same as conventional IMRT planning • For all target and normal tissue structures

  10. Helical Tomotherapy Treatment planning Tomotherapy Planning Parameters • Field Size in length : Jaw size • 5, 2.5 or 1 cm • Modulation factor • ratio of maximum leaf opening time to mean leaf opening time • Pitch

  11. The external beam radiotherapy and Image-guided radiotherapy (4) SomvilaiMayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University

  12. Helical Tomotherapy • Smaller field widths, smaller pitches and higher modulation factors Tomotherapy Planning Parameters More conformal plans But increased treatment time !!

  13. Helical Tomotherapy Image acquisition and matching • MVCT fan-beam images • In-plane resolution of 0.78 mm at the bore center ; mean beam energy = 0.75 MeV • Set up slices thickness of 2, 4 or 6 mm • ‘fine’, ‘normal’ and ‘coarse’ settings • The scan length is kept as short as possible • always within the region of the PTV

  14. Helical Tomotherapy Image matching

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